I would guess one or both thermostats is sticking open or the contacts are burned. Check for telltale soot or melted plastic on the thermostats. Also look for discolored wires which would indicate overheating due to high resistaance(burned contacts). The lower element could also be burned out, especially if when you do have hot water, you run out quicker than you should. Thermostats and elements are not very expensive.

My water heater needs to be reset constantly, I can hear it running and have to go and push the reset: button on it, if i hear it running, that means I have no hot water! This is very sporadic, sometimes it : doesn't happen for weeks or months then it starts doing it and last for weeks. What could be the problem.: It's a fairly new water heater - appx. 5 years old. It was installed by Sears and last year I had them come: out to check on this very problem and they couldn't find anything wrong with it. Any ideas! It's driving: me nuts!!